Method of reproducing speech and music by means of loudspeakers



1 A 0 t R g 6 e O .U N. m TS E 1 S NE m 3 a t v 9 WK 2 m m 2 Y? B D. KLEIS METHOD OF REPRODUCING SPEECH AND MUSIC BY MEANS OF LOUDSPEAKERS A ril 15, 1958 Filed 001:. 11, 1955 April 15, 1958 D. KLEIS METHOD OF REPRODUCING SPEECH AND MUSIC BY MEANS OF LOUDSPEAKERS Filed Oct. 11, 1955 2 Sheets-Sheet 2 IN VEN TOR DERK KLEIS' AGENT Unitcd States Patent METHOD OF REPRODUCING SPEECH AND MUSIC BY MEANS OF LOUDSPEAKERS Derk Kleis, Emmasingel, Eindhoven, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application October 11, 1955, Serial No. 539,908

Claims priority, application Netherlands October 18, 1954 2 Claims. (Cl. 179-1) This invention relates to methods of reproducing speech or music by means of loudspeakers radiating the sound to a listener in part directly and in part indirectly.

For obtaining a spatial effect it is already known to divide the acoustic frequency range that is transmitted into two or more ranges and to leave the reproduction thereof to a plurality of loudspeakers.

From U. S. patent specification 2,179,840 a reproducing device is already known in which the intermediate frequency and high-frequency ranges are reproduced by radiators which utilize the ceiling as a reflector, thus bringing about a more homogeneous distribution of the acoustic energy.

By means of experiments applicants have come to the recognition that not only the radiation of sound in different directions, but also the energy ratio between the direct sound and the indirect sound plays an important part in approaching the ideal sound reproduction. The term indirect sound is to be understood in this connection to mean the acoustic waves which are reflected by a real wall or virtual wall at least once before reaching the listeners cars. In contrast to a real acoustic obstacle the term virtual wall" is to be understood to mean the phenomenon which occurs when the radiation of an arbitrarily arranged loudspeaker 'is retarded with respect to another radiation, thus introducing reflection by a virtual wall as a result of a longer transit-time of the acoustic waves, which reflection is observed farther as the retardation is greater.

The method according to the invention is characterized in that in the reproduction of music at least the greater part of the acoustic energy is emitted indirectly, whereas in the reproduction of speech the greater part, as the case may be the total energy, is radiated directly.

it has been found that a listener who listens to the reproduction of music in a closed room, for example in a livingroom listens to a radio transmission, or in a cinema to a musical film, has a need by means of the sound received to localize the source thereof to a certain extent. For such localization it is necessary and has been found sufficient to cause a certain part, which is to be understood in this connection to be of the total acoustic energy or less, to be radiated directly and the remaining part, i. e. the greater .part, to be emitted indirectly.

On the other hand, on the ground of the above-mentioned recognition, a listener of a reproduction of music in a cinema in which the loudspeakers are arranged at certain distances from one another and in which the reproduction has no direct relationship with the projection image, has no need of any localization of the acoustic source. Consequently, in the method accord ing to the invention for such reproduction of music, the total acoustic energy is radiated indirectly.

On the contrary, in the case of speech and other acoustic effects, for example street noise in a play, special attention is paid to the audibility which is readily reduced by indirect sound, rather than to the spatial reproduction.

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In this case the aim will be to provide for a minimum indirect portion of the acoustic energy to be radiated.

It is already known to incorporate the loudspeakers for the direct and the indirect sound in one housing, for example a radio-cabinet, one or more loudspeakers being provided on the sides of the housing, for example for the emission of the high notes.

In a device for carrying out the method according to the invention, the housing advantageously comprises a switch which may be adjusted to the two energy ratios required for the reproduction of music and speech, respectively.

Such a switch permits of selecting and adjusting in a very simple manner the sound distribution which is optimum for the emission according to the character of the program transmitted.

In order that the invention may be readily carried into effect, it will now be described, by way of example, with reference to the embodiment shown in the accompanying drawing in which Fig. 1 shows a device for reproducing speech or music by means of loudspeakers and Fig. 2 shows the operating of the switch which divides the quantities of direct and indirect sound-energy.

In Figure 1 the speech or music reproduction by means of loudspeakers radiating the sound to the listener occurs in part directly from the loudspeaker 1 and in part indirectly by means of loudspeakers 2 and 3. The loudspeaker 1 is arranged on the front side of the housing 4 of the device, the loudspeakers 2 and 3 being arranged on the upper side and on the side of the housing, respectively. According to the invention, in the reproduction of music the greater part of the acoustic energy is emitted by the loudspeakers 2 and 3, whereas the reproduction of speech is radiated for the greater part by the loudspeaker 1.

In Figure 2 the sound energy from the receiver-circuits 4 feeds via the energy-ratio resister 6 and the switch 5 the loudspeakers 1, 2 and 3. In accordance with the invention this switch 5 has four positions.

I-l': the total speech reproduction is radiated directly by loudspeaker 1.

IIII: the greater part (f. i. of the speech-energy is radiated directly by loudspeaker 1, a small part (10%) indirectly by loudspeakers 2 and 3.

III-J11: the reproduction of music, the source of which 'must be located, is effected for a small part (f. i. 10%) directly and for the rest (90%) indirectly.

IV-IV: the reproduction of music, the source of which needs not be located, is completely indirect.

What is claimed is:

1. A sound system for reproducing music and speech, comprising a cabinet, a source of music and speech signals, a direct acoustical radiator arranged to radiate from said cabinet in a forwardly direction, an indirect acoustical radiator arranged to radiate from said cabinet in a direction other than forwardly, and a switch connected between said source of signals and said radiators, said switch having a music position whereby a relatively greater amplitude of said signals is applied to said indirect acoustical radiator and a speech position whereby a relatively greater amplitude of said signals is applied to said direct acoustical radiator.

2. A sound system for reproducing music and speech, comprising a cabinet, at source of music and speech sig nals, a direct acoustical radiator arranged to radiate from said cabinet in a forwardly direction, an indirect acoustical radiator arranged to radiate from said cabinet in a direction other than forwardly, and a switch having music and speech positions and connected between said source of signals and said radiators, said switch comprising an adjustableresistance element, means for in- References Cited in the file of this patent seriing 1 reiaiiveiy greater value of said resistar lce in UNITED STATES PATENTS- series w1th said chrect acoustlcal rad1ator when m the music position and means for inserting a relatively 2179840 Bufzky 52 greater value of said resistance in series with said indirect P 2474'191 Rad et a1 19 9 I.) acoustical radiator when in the speec position. 2573122 Weber 195] 

